java - Eclipselink 实体持续存在问题

Question

我正在通过一些在线教程学习 Eclipselink。当前在保留对象时遇到问题。

Exception in thread "main" java.lang.IllegalStateException: Exception Description: No transaction is currently active at org.eclipse.persistence.internal.jpa.transaction.EntityTransactionImpl.commit(EntityTransactionImpl.java:123) at com.training.service.EmployeePersistance.main(EmployeePersistance.java:23)

我使用 JPA 连接器的数据库连接工作正常。我已经通过执行

测试了连接

System.out.println(Persistence.createEntityManagerFactory("_EclipseLinkTraining").isOpen());

返回 true。数据库中未创建表。执行代码后，表会自动生成，但对象不会被持久化。以下是我造成问题的代码: 实体类:

@Entity
public class Employee {
    @Id
    int empId;

    @Basic(optional=true)
    String empName;

    //getters and setters
}

持久性.xml:

<persistence-unit name="_EclipseLinkTraining" transaction-type="RESOURCE_LOCAL">
    <class>com.training.entity.Employee</class>
    <properties>
        <property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/ecpliselink_training"/>
        <property name="javax.persistence.jdbc.user" value="root"/>
        <property name="javax.persistence.jdbc.password" value="root"/>
        <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver"/>
        <property name="eclipselink.ddl-generation" value="create-tables"/>
    </properties>
</persistence-unit>

java主方法:

public static void main(String[] args) {
    EntityManagerFactory factory = Persistence.createEntityManagerFactory("_EclipseLinkTraining");
    EntityManager manager = factory.createEntityManager();

    manager.getTransaction();

    Employee emp = new Employee();
    emp.setEmpId(1);
    emp.setEmpName("sam");
    manager.persist(emp);

    manager.getTransaction().commit();

    manager.close();
    factory.close();
    System.out.println("completed");
}

Answer 1

您正在获取事务，然后提交它，但您从未begun它。因此，正如消息所述，当前没有 Activity 的交易。